At the very centers of all large galaxies there lies a supermassive
black hole, a million to a billion times the mass of our Sun. 90%
of the time these supermassive black holes are quiet - emitting almost
no light from their close environs. But 10% of the time gas falling down
onto them heats up to extreme temperatures and emits light from X-rays to
the infrared, and 1% of the time some still mysterious process ejects
narrow jets of hot gas moving very close to the speed of light and emitting
strongly in radio waves.
HEA scientists study supermassive black holes in all these states, trying
to understand how they work.

Caption: Chandra X-ray observatory image of a jet a million
light-years long emitted from close to a supermassive black hole.
Yet this black hole has radio emission that is far younger than a
million years. Apparently these 'relativistic' jets turn on and off
repeatedly over cosmic history, but we do not yet know what the 'switch'
is that makes them shine at some times and not others.
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